Recently had trouble with my wife's 2007 Saturn Vue. It would crank but only run about 2 seconds before cutting off. Took it to a local GM repair shop where they replaced the ECM. We have only put about 300 miles on the car since this repair and it has started doing the same thing. I took it back to the same repair shop and now they say the ignition key cylinder is showing a fault and needs to be replaced. This requires the new key cylinder, new keys and programming ($500). Suggestions?

Honestly, sounds like 1st incident was security system related. Was security light blinking or was security icon on dash lit up? 2 second run time is quite typical for a car whose security system thinks it has been activated.

ECM problem? Possible but doubtful

They probably reset the security system, pulled the lock cyl and cleaned it up, and gave it back to you.

Find the ECM and see if you can get a date code or a picture of the area that would imply that no dirt or grime had been disturbed i e did they do the ecm replacement? If the date code on it is 2006 and it is filthy, the answer is no.

The ignition issue is likely real and is prob why your security system tripped.

There are multiple postings of the security reset procedures on the web. If this successfully solves your issue, then the cause of the malfunctioning security dytem may very well be the hey cyl.